Automobile braking energy recovery method considering driving style

Abstract

The invention discloses an automobile braking energy recovery method considering a driving style. The method comprises the steps that the driving style of a driver and the comfortable time headway of the corresponding style are determined; wherein the driving styles comprise aggressive styles, ordinary styles and prudent styles; when the real-time headway is larger than the safe headway, the current braking intention of the driver is recognized according to the current accelerator pedal position, the accelerator pedal change rate and the difference value of the real-time headway relative to the comfortable headway; the types of the braking intention comprise light degree, light-medium degree, medium strength and emergency; if the current braking intention of the driver is mild or mild, a regenerative braking strategy is adopted; if the current braking intention of the driver is moderate, a regenerative braking and mechanical braking mixed strategy is adopted; and if the current braking intention of the driver is emergency, a mechanical braking strategy is adopted. The driving intention recognition accuracy can be improved, so that the driving comfort and the braking energy recovery efficiency are improved.

Description

Technical Field

[0001] The invention relates to the field of electric vehicles, and in particular to a method for recovering automobile braking energy taking driving style into consideration. Background Art

[0002] The driving range is an important indicator of the performance of electric vehicles, and brake energy recovery is not only an important method to improve the driving range of electric vehicles, but also an important part of the energy management of new energy vehicles. Unlike traditional fuel vehicles, the braking process of electric vehicles includes two parts: motor braking and mechanical braking. Braking energy recovery means that during the braking process, electric vehicles give priority to using motors for braking, converting braking energy into electrical energy and storing it in energy storage devices, while providing regenerative braking force. This energy recovery method is of great significance to the energy saving and environmental protection of electric vehicles. Through brake energy recovery, electric vehicles can maximize the use of energy generated during braking, extend the driving range, and reduce dependence on external energy. This not only helps to improve the energy efficiency performance of electric vehicles, but also helps to reduce energy consumption and tail gas emissions, and has a positive impact on environmental protection.

[0003] At present, the most commonly used braking energy recovery method is to improve the energy recovery rate by adjusting the ratio of electric motor force and mechanical braking force. Its control strategy is usually divided into rule-based braking force distribution control strategy and optimization-based braking force distribution control strategy. Rule-based methods include formulating rules by identifying driving intentions, fuzzy rules, etc. This method has good real-time performance and strong practicality, but the effect is poor when facing more complex working conditions. Optimization-based methods include model predictive control, genetic algorithms, and particle swarm optimization. This method performs well in distribution effect, but has poor real-time performance and high computational cost.

[0004] People with different driving styles have different driving habits. Rules formulated with unified standards cannot guarantee the accuracy of driving intention recognition, nor can they guarantee that the car can achieve the best braking stability and braking energy recovery efficiency for different driving styles. Considering the driver's driving style in the braking strategy is one of the difficulties in future braking energy recovery. Summary of the invention

[0005] The present invention provides a method for automobile brake energy recovery taking driving style into consideration, which can improve the accuracy of driving intention recognition, thereby improving driving comfort, brake energy recovery efficiency and the cruising range of electric vehicles and improving economy.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: A method for automobile brake energy recovery taking into account driving style, comprising: Step 1, determining the driver's driving style and the comfortable headway time corresponding to the style; wherein the driving style includes aggressive, normal and cautious; Step 2, when the real-time headway is greater than the safe headway, identifying the driver's current braking intention according to the current accelerator pedal position, the accelerator pedal change rate, and the difference between the real-time headway and the comfortable headway; the types of braking intention include: mild, mild-moderate, medium-intensity, and emergency; Step 3: If the driver's current braking intention is mild or mild to moderate, a regenerative braking strategy is adopted; If the driver's current braking intention is of medium intensity, a hybrid strategy of regenerative braking and mechanical braking is adopted; If the driver's current braking intention is urgent, a mechanical braking strategy is adopted; Among them, the cost function of the hybrid strategy of regenerative braking and mechanical braking includes two parts: braking energy recovery rate and braking stability, and different weight coefficients are assigned for different driving styles: for aggressive drivers, the weight of braking stability is higher than the weight of braking energy recovery rate; for cautious drivers, the weight of braking energy recovery rate is higher than the weight of braking stability; for ordinary drivers, the weights of braking energy recovery rate and braking stability are the same.

[0007] Furthermore, a large amount of historical driving data of various types of drivers is referred to and a clustering algorithm is used to determine the driver's driving style; the types of historical driving data include: headway, average deceleration, average acceleration, average accelerator pedal position and accelerator pedal change rate.

[0008] Furthermore, the principal component analysis method is first used to reduce the dimension of each historical driving data, and then the K-Medoids clustering algorithm is used to classify the drivers corresponding to each historical driving data into three categories: aggressive, ordinary and cautious.

[0009] Furthermore, the headway time refers to the time it takes for the vehicle to travel from its position to the position of the preceding vehicle, which is expressed as: ; Different styles of comfortable headway time are set based on the different speeds of the vehicle.

[0010] Furthermore, if it is determined that the current real-time headway is less than the safe headway, or it is determined that the current real-time vehicle speed exceeds a preset value, or the charge state of the regenerative braking battery exceeds a preset value, or the brake pedal position is not 0, the driver's braking intention is directly identified as emergency; otherwise, fuzzy logic rules are established to identify the following types of driver's braking intentions: mild, mild-moderate, and medium-intensity; The fuzzy logic rules include inputs of the current accelerator pedal position, the accelerator pedal change rate, and the difference between the real-time headway and the comfortable headway, and outputs three types of braking intentions: mild, mild-moderate, and medium-intensity.

[0011] Furthermore, if the driver's current braking intention is mild, when the regenerative braking strategy is adopted, the total torque required by the vehicle is provided entirely by the regenerative braking force of the front wheels; If the driver's current braking intention is mild or moderate, when the regenerative braking strategy is adopted, the regenerative braking force of the front wheels and the regenerative braking force of the rear wheels jointly provide the total torque required by the vehicle; If the driver's current braking intention is emergency, when the mechanical braking strategy is adopted, the front axle mechanical brake and the rear axle mechanical brake jointly provide the total torque required by the vehicle.

[0012] Furthermore, the cost function of any braking strategy is uniformly expressed as the following multi-objective optimization cost function:

[0013]

[0014]

[0015] In the formula, are the weight coefficients of braking stability and braking energy recovery rate respectively; is the distribution coefficient of the front and rear axle braking torque, that is , is the total torque required by the vehicle, is the front axle braking torque; is the ideal distribution coefficient of the front and rear axle braking torque, is the regenerative braking torque, represents the ideal charging torque; is the longitudinal distance from the vehicle's center of gravity to the rear axle, is the front and rear wheelbase, Indicates braking intensity; is the height of the vehicle's center of gravity; Represents the maximum charging torque of the battery, Represents the maximum charging torque of the total motor.

[0016] Furthermore, the constraints of any braking strategy include: (1) The total regenerative braking torque cannot exceed the maximum charging torque of the motor, and the maximum charging torque of each motor cannot exceed the maximum charging torque of each motor.

[0017]

[0018]

[0019] In the formula, is the regenerative braking torque of the front axle, is the regenerative braking torque of the rear axle, and Respectively represent the maximum charging torque of the front axle motor and the rear axle motor; (2) The regenerative braking torque cannot exceed the total braking torque, and the front axle regenerative braking torque cannot exceed the total regenerative braking torque:

[0020]

[0021] In the formula, is the proportion coefficient of regenerative braking torque, that is , If regenerative braking strategy is adopted, If a hybrid strategy of regenerative braking and mechanical braking is adopted, If a mechanical braking strategy is adopted, ; is the proportion coefficient of the front axle regenerative braking torque, that is , is the regenerative braking torque of the front axle; (3) For mild braking intention and mild to moderate braking intention, the front and rear axle braking force distribution coefficient is calculated according to the braking regulations. Braking strength The following conditions need to be met: (0≤z≤0.3) (0.15≤z≤0.3) For medium-intensity braking intentions, the front and rear axle braking force distribution coefficients are based on the braking regulations. Braking strength The following conditions must be met (0.15≤z≤0.3) (0.2≤z≤0.8) Among them, the braking intensity It is expressed by the ratio of braking deceleration to gravity acceleration. , are the longitudinal distances from the center of gravity to the front axle and the rear axle respectively; is the wheelbase, ; is the height of the vehicle's center of gravity.

[0022] Compared with the existing braking energy recovery method, the present invention has the following advantages: 1. The rate of change of releasing the accelerator pedal is used as one of the inputs of the fuzzy logic control rule, which solves the problem of low energy recovery caused by low frequency of the driver pressing the brake pedal when driving a car in single-pedal mode.

[0023] 2. By considering driving style factors, the concept of comfortable (habitual) headway time is introduced on the basis of the original fuzzy logic control, which improves the accuracy of identifying the braking intentions of different drivers and thus improves driving comfort.

[0024] 3. By matching personalized braking force distribution strategies to three different driving styles and performing targeted optimization, the braking energy can be recovered as much as possible while ensuring braking efficiency, thereby increasing the range of electric vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram of a method for identifying a driver's braking intention according to an embodiment of the present application; Figure 2 It is a flow chart of the braking energy recovery method described in an embodiment of the present application. DETAILED DESCRIPTION

[0026] The following is a detailed description of an embodiment of the present invention. This embodiment is based on the technical solution of the present invention, and provides a detailed implementation method and a specific operation process to further explain the technical solution of the present invention.

[0027] This embodiment provides a method for automobile braking energy recovery taking into account driving style, referring to Figure 1 , 2 As shown, including: Step 1, determining the driver's driving style and the comfortable headway time of the corresponding style; wherein the driving style includes aggressive, normal and cautious.

[0028] By referring to a large amount of historical driving data of various types of drivers, including headway, average deceleration, average acceleration, average accelerator pedal position and accelerator pedal change rate, a clustering algorithm is used to determine the driver's driving style.

[0029] First, the principal component analysis (PCA) method is used to reduce the dimension of each historical driving data, and then the K-Medoids clustering algorithm is used to classify the drivers corresponding to each historical driving data into three driving styles: aggressive, ordinary and cautious.

[0030] The headway time refers to the time interval between the two vehicles passing the same position during the driving process, that is, the time it takes for the vehicle to travel from its position to the position of the preceding vehicle, which can be specifically expressed as: ; Based on the historical driving data of the following distances of the three driving styles during multiple driving processes, the comfortable (habitual) headway time of the three driving styles is obtained through frequency analysis. The comfortable headway time of the aggressive type is recorded as , the comfortable headway for an average driver is recorded as , the comfortable headway for cautious drivers is recorded as .

[0031] Step 2, identifying the driver's current braking intention: when the real-time headway is greater than the safe headway, identifying the driver's current braking intention based on the current accelerator pedal position, the accelerator pedal change rate, and the difference between the real-time headway and the comfortable headway; the types of braking intention include: mild, mild-moderate, medium-intensity, and emergency.

[0032] Emergency braking means that the driver releases the accelerator pedal and slams on the brake pedal in an emergency situation, and needs to immediately reduce the vehicle speed to 0. At this time, the required braking force and braking deceleration are very large. Emergency braking is a special case, and its triggering condition is that the accelerator pedal position is 0 and the brake pedal position changes. Therefore, when such conditions are met, the driving intention is considered to be emergency braking.

[0033] In addition, if it is determined that the current real-time headway is less than the safe headway, or the current real-time vehicle speed exceeds a preset value, or the charge state of the regenerative braking battery exceeds a preset value, the driver's braking intention is also directly identified as emergency.

[0034] If the following conditions need to be met, fuzzy logic rules are established to identify several other braking intentions of the driver.

[0035] (1) The real-time headway is greater than the safe headway.

[0036] When the real-time headway is less than the safe headway, the vehicle is in a dangerous driving situation. At this time, the largest possible braking force is needed to keep the vehicle in a safe state. At this time, providing pure mechanical braking force is a better choice. Referring to the research of existing scholars, when the headway is less than 0.6s, the vehicle is in a dangerous driving state, so this embodiment sets the minimum safe headway to 0.6s.

[0037] (2) The real-time vehicle speed is greater than 10 m / s.

[0038] (3) The real-time SOC of the regenerative braking battery is less than 90%. When SOC>90%, the corresponding braking force is still provided according to the required braking intensity. In order to reduce the battery SOH loss, the required braking force is provided entirely by mechanical braking force, and regenerative braking force is no longer provided.

[0039] (4) The brake pedal is not engaged.

[0040] The recognition of braking intention for three different driving styles is carried out separately. Taking fuzzy logic control as an example, the accelerator pedal position , accelerator pedal change rate , real-time headway and comfortable headway (aggressive type is , the common type is , cautious type ) is used as the input of the fuzzy logic controller, the accelerator pedal change rate , Press the accelerator pedal for a long time for the next step. The driver's braking intention is output, which includes light braking, light-moderate braking and moderate braking. Different braking intentions correspond to different braking intensity ranges. Taking fuzzy logic as an example, the specific fuzzy logic rules are as follows: Accelerator pedal opening {zero (Z), small (S), medium (M), large (L)}; Accelerator pedal change rate { negative small (NS), negative medium (NM), negative large (NL), zero (Z)}; Distance comfortable following distance {zero (Z), negative small (NS), negative medium (NM), negative large (NL)}; Driving intention {slow acceleration (SA), normal acceleration (NA), rapid acceleration (RA), coasting (GL), slow deceleration (SB), normal deceleration (NB), rapid deceleration (RB)}; among which slow deceleration (SB), normal deceleration (NB), rapid deceleration (RB) in driving intention correspond to mild, mild-medium and medium-intensity in braking intention.

[0041] This fuzzy rule is mainly used to identify the driver's braking intention. The positive change of the accelerator pedal reflects the driver's acceleration intention, so the accelerator pedal change rate only identifies the negative change rate. The distance to the comfortable headway represents the difference between the real-time headway and the comfortable headway. Z represents that the driver is currently in a comfortable following headway. NL represents that the driver's current following headway is very close to the safe following headway. If the driver's headway at this time is greater than the comfortable following headway, without stepping on the brake pedal, the driver's driving intention is more inclined to accelerate to the comfortable following headway, so this situation is not considered in the fuzzy rule. The fuzzy rules in this embodiment are specifically shown in Table 1:

[0042] The different braking intentions in this article are explained as follows: Light braking means that the driver intends to maintain the speed or slowly reduce the speed. At this time, only a small braking force and braking deceleration are required. The corresponding braking intensity z range is 0 <z<0.1。

[0043] Light to moderate braking means that the driver intends to reduce the current speed. At this time, a moderate braking force and braking intensity are required. The corresponding braking intensity z range is 0.1 <z<0.2。

[0044] Medium-intensity braking means that the driver intends to quickly reduce the current vehicle speed. At this time, a medium-to-high braking force and braking intensity are required. The corresponding braking intensity z range is 0.2 <z<0.7。

[0045] Emergency braking means that when the driver encounters an emergency, he releases the accelerator pedal and slams on the brake pedal, and needs to immediately reduce the vehicle speed to 0. At this time, the required braking force and braking deceleration are very large. Emergency braking is a special situation, and its triggering conditions are that the accelerator pedal position is 0 and the brake pedal position changes.

[0046] Step 3: adopt a corresponding braking strategy according to the driver's current braking intention.

[0047] (1) Light braking: If the driver's current braking intention is light braking, the regenerative braking strategy is adopted.

[0048] When the driver is identified as having a light braking intention, the required braking force is small and can be provided by the regenerative braking force of the front wheels. In order to maximize energy recovery, the required braking force is all provided by the regenerative braking force of the front wheels, that is, , , ,in is the total torque required, is the total regenerative braking torque, Regenerative braking force for the front axle. is the total mechanical braking torque, braking force distribution coefficient .

[0049] (2) Light to moderate braking: If the driver's current braking intention is light to moderate braking, a regenerative braking strategy is adopted.

[0050] When the driver's moderate braking intention is identified, the front wheel regenerative braking force cannot meet the required braking force. Under the premise of ensuring safety and maximizing energy recovery, the rear wheel regenerative braking force intervenes. ,in is the regenerative braking torque of the rear axle, , is the front axle regenerative braking ratio, , is the regenerative braking force ratio, braking force distribution coefficient .

[0051] (3) Medium-intensity braking: If the driver's current braking intention is medium-intensity braking, a hybrid strategy of regenerative braking and mechanical braking is adopted.

[0052] When the driver is identified as intending to brake with medium intensity, the regenerative braking force of the front and rear wheels cannot meet the required braking force. Under the premise of ensuring safety, the mechanical braking force is used to maximize energy recovery. , , ,in is the front axle mechanical brake torque, is the rear axle mechanical braking torque, mechanical braking force distribution coefficient , braking force distribution coefficient .

[0053] (4) Emergency braking: If the driver's current braking intention is emergency braking, a mechanical braking strategy is adopted.

[0054] When the driver is identified as intending to perform emergency braking, the required braking force is large and the braking situation is urgent. Since the regenerative braking force reacts relatively slowly, the required regenerative braking force is fully provided by the mechanical braking force. , , , , Braking force distribution coefficient .

[0055] Constraints and cost functions of various braking strategy optimization models in embodiments of the present invention.

[0056] 1. Restrictions The limiting conditions of the braking strategy in the embodiment of the present invention include: (1) The total regenerative braking torque cannot exceed the maximum charging torque of the motor, and the maximum charging torque of each motor cannot exceed the maximum charging torque of each motor.

[0057]

[0058]

[0059] In the formula, is the regenerative braking torque of the front axle, is the regenerative braking torque of the rear axle, and Respectively represent the maximum charging torque of the front axle motor and the rear axle motor; (2) The regenerative braking torque cannot exceed the total braking torque, and the front axle regenerative braking torque cannot exceed the total regenerative braking torque:

[0060]

[0061] In the formula, is the proportion coefficient of regenerative braking torque, that is , If regenerative braking strategy is adopted, If a hybrid strategy of regenerative braking and mechanical braking is adopted, If a mechanical braking strategy is adopted, ; is the proportion coefficient of the front axle regenerative braking torque, that is , is the regenerative braking torque of the front axle; (3) For mild braking intention and mild to moderate braking intention, the front and rear axle braking force distribution coefficient is calculated according to the braking regulations. Braking strength The following conditions need to be met: (0≤z≤0.3) (0.15≤z≤0.3) For medium-intensity braking intentions, the front and rear axle braking force distribution coefficients are based on the braking regulations. Braking strength The following conditions must be met (0.15≤z≤0.3) (0.2≤z≤0.8) The braking intensity is expressed by the ratio of braking deceleration to gravity acceleration. , are the longitudinal distances from the center of gravity to the front axle and the rear axle respectively; is the wheelbase, ; is the height of the vehicle's center of gravity.

[0062] 2. Cost Function Since the braking force is completely provided by the front axle regenerative braking force during light braking, and completely provided by the mechanical braking force during heavy braking, the optimization model of this embodiment is only used for light, medium and medium-intensity braking, and does not include the optimization of light and heavy braking. This optimization mathematical model proposes two optimization goals, namely, optimal braking stability and maximum regenerative braking efficiency.

[0063] (1) Optimal braking stability During braking, it is not allowed for the rear wheels to lock before the front wheels, as this will cause the vehicle to lose stability. On the contrary, locking the front and rear wheels at the same time can achieve the best braking stability. In this case, the distribution of braking force follows the ideal braking force curve, also known as the I curve, at this time:

[0064] The following cost function is established to optimize the braking force distribution to obtain the best braking stability:

[0065] (2) Maximum regenerative braking efficiency In order to achieve the maximum regenerative braking efficiency, the ideal charging torque needs to be achieved. The ideal charging torque is determined by the minimum value of the maximum charging torque of the battery and the maximum charging torque of the motor, that is:

[0066] In the formula Represents the maximum charging torque of the battery, Represents the maximum charging torque of the motor. When the braking energy of the present invention is recovered, it is fed back to charge the battery. The battery is responsible for providing electrical energy to the motor. The motor, as an energy conversion device, converts the electrical energy provided by the battery into mechanical energy.

[0067] The following cost function is established to optimize the ideal charging torque to obtain the maximum regenerative braking efficiency:

[0068] For regenerative braking, multi-objective optimization is required to optimize these two objectives at the same time. Multi-objective optimization refers to finding the optimal solution so that these objective functions can reach the optimal or near-optimal state when there are multiple conflicting objective functions in the optimization problem. In multi-objective optimization, there is no longer only a single optimization objective, but multiple independent and potentially conflicting optimization objectives. The goal of multi-objective optimization is to make these solutions reach the optimal or near-optimal state on multiple objective functions, rather than just pursuing the optimal solution on a single objective function. Commonly used multi-objective algorithms include genetic algorithms, particle swarm algorithms, and gray wolf algorithms, etc. You can choose any one of these optimization algorithms.

[0069] Therefore, the multi-objective optimization cost function established in the embodiment of the present invention is:

[0070] In the formula and They are the weight coefficients of braking stability and energy recovery rate. By adjusting the weight coefficients according to the driving style, braking stability and energy recovery can be better balanced.

[0071] The weight coefficient adjusted according to the driving style can be determined based on the existing driving data. For aggressive drivers, they usually drive at a faster speed and have a relatively high deceleration when braking. Therefore, for safety reasons, in a more preferred embodiment, a higher weight can be given to braking stability, that is, For cautious drivers, their driving speed is relatively slow and the braking deceleration is relatively low. In this case, the energy recovery rate can be given a higher weight, that is, , in order to maximize the effect of energy recovery.

[0072] The above embodiments are preferred embodiments of the present application. Ordinary technicians in this field can also make various changes or improvements on this basis. Without departing from the overall concept of the present application, these changes or improvements should fall within the scope of protection required by the present application.

Claims

1. A method for automobile braking energy recovery taking into account driving style, characterized in that: include: Step 1, determining the driver's driving style and the comfortable headway time corresponding to the style; wherein the driving style includes aggressive, normal and cautious; Step 2, when the real-time headway is greater than the safe headway, identifying the driver's current braking intention according to the current accelerator pedal position, the accelerator pedal change rate, and the difference between the real-time headway and the comfortable headway; the types of braking intention include: mild, mild-moderate, medium-intensity, and emergency; Step 3: If the driver's current braking intention is mild or mild to moderate, a regenerative braking strategy is adopted; If the driver's current braking intention is of medium intensity, a hybrid strategy of regenerative braking and mechanical braking is adopted; If the driver's current braking intention is urgent, a mechanical braking strategy is adopted; Among them, the cost function of the hybrid strategy of regenerative braking and mechanical braking includes two parts: braking energy recovery rate and braking stability, and different weight coefficients are assigned for different driving styles: for aggressive drivers, the weight of braking stability is higher than the weight of braking energy recovery rate; for cautious drivers, the weight of braking energy recovery rate is higher than the weight of braking stability; for ordinary drivers, the weights of braking energy recovery rate and braking stability are the same.

2. The method for automobile braking energy recovery considering driving style according to claim 1, characterized in that: By referring to a large amount of historical driving data of various types of drivers and using clustering algorithms to determine the driving style of the drivers; The types of historical driving data include: headway, average deceleration, average acceleration, average accelerator pedal position and accelerator pedal change rate.

3. The method for automobile braking energy recovery considering driving style according to claim 2, characterized in that: Firstly, principal component analysis is used to reduce the dimensionality of each historical driving data, and then the K-Medoids clustering algorithm is used to classify the drivers corresponding to each historical driving data into three categories: aggressive, ordinary and cautious.

4. The method for automobile braking energy recovery considering driving style according to claim 1, characterized in that: Headway refers to the time it takes for the vehicle to travel from its position to the position of the vehicle ahead, expressed as: ; Different styles of comfortable headway time are set based on the different speeds of the vehicle.

5. The method for automobile braking energy recovery considering driving style according to claim 1, characterized in that: If it is determined that the current real-time headway is less than the safe headway, or the current real-time vehicle speed exceeds a preset value, or the charge state of the regenerative braking battery exceeds a preset value, or the brake pedal position is not 0, the driver's braking intention is directly identified as emergency; Otherwise, fuzzy logic rules are established to identify the following types of driver's braking intentions: mild, mild-moderate, and moderate; The fuzzy logic rules include inputs of the current accelerator pedal position, the accelerator pedal change rate, and the difference between the real-time headway and the comfortable headway, and outputs three types of braking intentions: mild, mild-moderate, and medium-intensity.

6. The method for automobile braking energy recovery considering driving style according to claim 1, characterized in that: If the driver's current braking intention is mild, when the regenerative braking strategy is adopted, the total torque required by the vehicle is provided entirely by the regenerative braking force of the front wheels; If the driver's current braking intention is mild or moderate, when the regenerative braking strategy is adopted, the regenerative braking force of the front wheels and the regenerative braking force of the rear wheels jointly provide the total torque required by the vehicle; If the driver's current braking intention is emergency, when the mechanical braking strategy is adopted, the front axle mechanical brake and the rear axle mechanical brake jointly provide the total torque required by the vehicle.

7. The method for automobile braking energy recovery considering driving style according to claim 1, characterized in that: The cost function of any braking strategy is uniformly expressed as the following multi-objective optimization cost function: ； ； ； In the formula, are the weight coefficients of braking stability and braking energy recovery rate respectively; is the distribution coefficient of the front and rear axle braking torque, that is , is the total torque required by the vehicle, is the front axle braking torque; is the ideal distribution coefficient of the front and rear axle braking torque, is the regenerative braking torque, represents the ideal charging torque; is the longitudinal distance from the vehicle's center of gravity to the rear axle, is the front and rear wheelbase, Indicates braking intensity; is the height of the vehicle's center of gravity; Represents the maximum charging torque of the battery, Represents the maximum charging torque of the total motor.

8. The method for automobile braking energy recovery taking driving style into consideration according to claim 7, characterized in that: The constraints of any braking strategy include: (1) The total regenerative braking torque cannot exceed the maximum charging torque of the motor, and the maximum charging torque of each motor cannot exceed the maximum charging torque of each motor. ； ； ； In the formula, is the regenerative braking torque of the front axle, is the regenerative braking torque of the rear axle, and Respectively represent the maximum charging torque of the front axle motor and the rear axle motor; (2) The regenerative braking torque cannot exceed the total braking torque, and the front axle regenerative braking torque cannot exceed the total regenerative braking torque: ； ； In the formula, is the proportion coefficient of regenerative braking torque, that is , If regenerative braking strategy is adopted, If a hybrid strategy of regenerative braking and mechanical braking is adopted, If a mechanical braking strategy is adopted, ; is the proportion coefficient of the front axle regenerative braking torque, that is , is the regenerative braking torque of the front axle; (3) For mild braking intention and mild to moderate braking intention, the front and rear axle braking force distribution coefficient is calculated according to the braking regulations. Braking strength The following conditions need to be met: (0≤z≤0.3)； (0.15≤z≤0.3)； For medium-intensity braking intentions, the front and rear axle braking force distribution coefficients are based on the braking regulations. Braking strength The following conditions must be met (0.15≤z≤0.3)； (0.2≤z≤0.8)； Among them, the braking intensity It is expressed by the ratio of braking deceleration to gravity acceleration. , are the longitudinal distances from the center of gravity to the front axle and the rear axle respectively; is the wheelbase, ; is the height of the vehicle's center of gravity.

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